The present invention is related to an inspection jig and a contact probe incorporated in the jig, which firmly connect an inspection apparatus to an inspected device in a case where an electric characteristic of this device is inspected before the device is assembled on a circuit board. The inspected device corresponds to either a module or an IC (integrated circuit) of a high frequency/high-speed circuit such as, for instance, an amplifier circuit, a mixer circuit, and a filter circuit, which are assembled in a cellular phone.
In this specification, the above-described high frequency circuit is defined as such an analog circuit operable in a high frequency range, and the above-described high-speed circuit is defined as such a digital circuit in which a pulse width and a pulse interval of a digital signal are very short, and further, both the analog high frequency circuit and the digital high-speed circuit will also be referred to as an RF (radio frequency) circuit or device. The RF signal involves either a sine wave signal, or a pulse signal, the repetition period of which is higher than, or equal to 1 GHz.
In a case where electric characteristics of RF devices such as semiconductor wafers, ICs, and modules are inspected, in particular, if contact conditions of terminal portions are not sufficiently established, then impedances or the like are changed, so that measurement values are varied. Therefore, the electric characteristics of the RF devices are inspected by way of a jig shown in FIG. 4 as disclosed in Japanese Patent Publication No. 2001-99889A.
Specifically, an RF circuit corresponding to the inspected device is arranged as a module 20 in which an amplifier circuit, a mixer circuit, or the like are assembled within a housing made of a metal material in order to avoid external. The module 20 is constituted by employing input/output terminals 21/24 for inputting/outputting RF signals, a power supply terminal 22, a ground (earth) terminal 23, or the like on a surface of this metal housing. Then, such an inspection method is employed so as to inspect the RF circuit in such a manner that these terminals 21, 22, 23, 24 are electrically connected to respective terminals of a wiring board 36 on which wiring lines for inspection have been formed.
In the above inspection jig, it is employed a contact probe in which a plunger and a spring are inserted into a metal pipe such that a tip end of the plunger is retractably projected from the pipe by the urging force of the spring. A contact probe 33 for RF signal, a contact probe 34 for power supply, and a contact probe 35 for ground are stored within a metal block 31 capable of preventing an adverse influence caused by noise. These contact probes 33, 34, 35 are electrically made in contact with the respective terminals 22/23 and input/output terminals 21/24.
This contact probe 33 for RF signal is made of a short-length probe so as to decrease an inductance component. Even when this contact probe 33 for RF signal employs such a short probe, the inductance component of this short contact probe 33 cannot be neglected in the RF range. For example, as to a contact probe for RF signal having an inductance value of 1 nH, an impedance of this 1 nH—contact probe becomes 63 Ohms (Ω) in the frequency range of 10 GHz. To avoid such a problem, while a dielectric tube is inserted between the contact probe 33 for RF signal and the metal block 31, a coaxial line structure is formed in such a way that the contact probe 33 for RF signal is set as a core conductor and the metal block 31 is set as an external conductor. As a result, this coaxial line structure may prevent the increase of the impedance, and/or may avoid the penetration of the noise. In FIG. 4, reference numeral 37 shows a coaxial cable, and reference numeral 38 represents a plate for fixing the metal pipe provided as an outer periphery of the contact probe 33.
In the inspection jig shown in FIG. 4, two sets (input and output purposes) of the contact probes 33 for RF signals are illustrated, and one set of the contact probe 34 for power supply and also one set of contact probe 35 for ground are illustrated. However, in actual inspection jigs, large members of these contact probes are formed. Moreover, in the specific case, there are some cases that approximately 400 pieces per 1 cm2 of terminals are provided in conjunction with recent higher integrations such as ICs. Therefore, such narrower pitches (about 0.4 mm) of the respective terminals appear in the field.
When terminal pitches become such narrower pitches, an outer diameter of a contact probe for RF signal, which involves a dielectric layer, must be made narrow. However, this outer diameter must be matched with such a characteristic impedance (for example, 50 Ω) which satisfies a relationship (1) between a diameter “d” of a core conductor of a coaxial line path and an inner diameter “D” of an outer conductor thereof, assuming now that a dielectric constant of a dielectric substance between the core conductor and the external conductor is defined as “∈r”.                               Z          ⁢                                           ⁢                      o            ⁡                          (              Ω              )                                      =                              138.15                                          ɛ                r                                              ⁢                      log            10                    ⁢                      D            d                                              (        1        )            In order to satisfy this formula (1), since a material whose dielectric constant is small is employed as a dielectric substance, the inner diameter “D” of the outer conductor can be decreased. However, even when a tube made of polytetrafluoroethlene is employed, and also a contact probe having the narrowest outer diameter (=0.15 mm) is employed so as to satisfy this formula (1), an inner diameter of an outer conductor (namely, inner diameter of through hole formed in metal block) becomes approximately 0.5 mm in order that a characteristic impedance of a coaxial line path becomes 50Ω. As a result, this inner diameter of the outer conductor cannot be fitted to the pitch of 0.4 mm. The above-described tube made of polytetrafluoroethlene, the dielectric constant of which is equal to 2.1, is presently known as such a dielectric substance having the smallest dielectric constant.
As a consequence, in order to simply make an outer diameter narrower, a diameter of a core conductor is required to be made smaller, and an outer diameter of a contact probe must be made narrower, for example, about 0.09 mm (in this case, inner diameter “D” becomes 0.3 mm). In order to narrow a contact probe having a complex structure, there are such problems that very high cost is required, durability of the contact probe is lowered, and reliability of this contact probe is decreased.